Electronic trip units (trip units) for actuating the separable contacts in a circuit breaker are well known. An electronic trip unit typically comprises current sensors and may include voltage sensors that provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals that are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality trip setting values, including initializing parameters, boot code, and operational parameters (e.g., trip setting instructions). Operational parameters for the application code are also stored in the EEPROM. An output of the electronic trip unit actuates a trip module, such as a solenoid that trips a mechanical operating mechanism. The mechanical operating mechanism, in turn, separates a pair of main contacts within the circuit breaker. When the contacts open, circuit current is prevented from flowing from one contact to the other, and electrical current is prevented from flowing to a load that is connected to the breaker. The electronic trip unit initiates a trip for instantaneous, short time, long time, ground fault and manual conditions.
Circuit Breakers having electronic trip units are described in U.S. Pat. No. 4,672,501 entitled xe2x80x9cCircuit Breaker and Protective Relay Unitxe2x80x9d. Such trip units often include a keypad along with a display for accessing the processor and for entering and changing the trip unit settings. One such circuit breaker having a keypad and display is described within U.S. Pat. No. 4,870,531 entitled xe2x80x9cCircuit Breaker With Removable Display and Keypadxe2x80x9d.
Remote setting of a circuit breaker is desirable to customers who would like to be able to adjust set points of multiple breakers from a single workstation. One such circuit breaker having a local keypad and display with remote setting capability is described within U.S. Pat. No. 5,019,956 entitled xe2x80x9cPower Control Apparatus.xe2x80x9d However, the circuit breaker described in U.S. Pat. No. 5,019,956 does not display the settings if there is no power to the trip unit.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a trip unit including a sensor for sensing a condition of a circuit providing electricity to a load and a signal converter for converting signals generated by the sensor into a digital value indicative of the condition, and further comprising: a first storage device including a first trip setting value stored therein; a second storage device including a second trip setting value stored therein; a switch for selecting from the first and second trip setting values; and a microcontroller including an output generating a trip signal in response to the digital value indicative of the condition in the circuit and one of the first and second trip setting values selected by the switch.